Rotary blasting machines have become standard equipment for processing metal surfaces to remove scale, and in preparation for the application of coatings of various types. In summary, these machines project a high velocity stream of abrasive particles at the target, the velocity being generated by a rotor shaped somewhat like a paddle wheel. The abrasive particles are fed into the central portion of the rotor at a selected point to establish a particular direction of the tangential stream emerging at the periphery of the rotor. These machines have evolved a fairly standard feeding mechanism that receives the bulk abrasive material, and distributes it at a uniform rate in to the area swept by a set of blades mounted on the rotor in a generally radial position with respect to the axis of rotation. These blades present flat or slightly curved surfaces close to a radial plane containing this axis of rotation, and these active surfaces of the blades are subject to violent erosion as the machine continues to operate. These conditions have resulted in the manufacture of these blades as replacable components of an extremely hard alloy. The need for frequent replacement, and the cost of the alloy material, have resulted in a strong need for a blademounting system that is secure enough to handle the centrifugal forces involved, and positive enough in placement of the blades to assure continuation of the most effective operating position.
A common type of rotor design uses a single plate mounted on a hub secured to a shaft rotating in conventional bearings, and adapted to receive power through a standard belt drive system. The plate is positioned in a plane perpendicular to the axis of rotation, and carries a set of brackets providing support for the blades. The blades have projections interengaging with these brackets to resist the action of centrifugal force, and a locking system is always incorporated to maintain the interengagement of the blades and the brackets. As thus broadly defined, such machines are conventional.
One of the problems involved in these machines is the tendency for abrasive particles to accumulate at the junction between the blades and the brackets, to the point that the position of the blade is distorted. This problem is dealt with in Application Ser. No. 465,550 (assigned to the same assignee as the present application), filed on Apr. 30, 1974, now U.S. Pat. No. 3,894,360, issued July 15, 1975, by shielding the inner extremity of the junction between the brackets and blades to at least protect this junction from the direct stream of abrasive particles. A substantial percentage of these particles, however, may be considered as moving in a random pattern at very high velocities, as a result of rebounding from the many surfaces on the rotor, blades, and feeding mechanism. This random movement has inevitably resulted in the eventual accumulation of particles between the blade and the bracket, although the shielding of the inner extremity has the effect of vastly reducing the rate of accumulation. It would be very desirable to not only further reduce this tendency, but eliminate it entirely.